This invention relates to a stop device for the spindles of a textile spinning machine.
In a textile spinning machine, such as a ring spinning machine, it is known that the effective production expressed in kilograms of thread, for example cotton thread, is determined by the difference between the theoretical production, calculated on the basis of the thread production rate, and the production loss, ie the lack of transformation of the silver into thread.
The effective production of the machine obviously represents the basis for costing the sold thread.
The factor mostly responsible for the production loss of the spinning machine is the thread breakage due to the pull on the fibres during the winding to form bobbins. Such breakage depends on environmental factors such as humidity and temperature of the working environment, and systemic parameters such as irregular or untimely ordinary or extraordinary maintenance of the machine. The rejoining of the broken thread, whether done manually or automatically, inevitably requires the stoppage of the spindle or spindles involved in the breakage.
To stop the spindles, devices are used in which an operating lever acts on a brake piston carrying a brake shoe which engages the shank of the spindle, so braking it. The action of the lever is opposed by a return spring, which returns the device into its inactive position when the action on the lever ceases.
The spindles are rotated by a belt by tangential contact with the spindle shanks, this contact being maintained by tensioning members in the form of rollers positioned at intervals along the path of the drive belt on that side of it distant from the spindles. The spindles are rotatably supported with their axis vertical in the fixed structure of the machine and are arranged to receive tubes on which the thread is wound.
The brake shoe acts on the spindle shank substantially on the opposite side to that in contact with the drive belt. The intensity of the braking action on the spindle is determined, in the current state of the art, by the intensity of the pressure which the operator exerts on the operating lever, which is accessible from the outside of the spinning machine. The operator exerts this action by means of his knee as he has to keep both hands free to be able to join the broken thread. The braking action applied in this manner is therefore extremely variable and tends to be very intense in order to ensure that the spindle halts rapidly and then remains halted, even though it remains in tangential contact with the drive belt, which slides along the shank of the braked spindle.
In traditional spindles of essentially rigid construction, a too high braking pressure does not result in any substantial problems, except perhaps an excessive load on the radial bearing supporting the spindle rod, which with time may lead to damage or centering irregularity.
The use of the more developed spindles known as "elastic" spindles can however result in serious problems when used with the described traditional stop devices. This is because these spindles have a special structure comprising inserts of materials with relative flexibility, to reduce vibration transmission to the machine, and hence reduce the noise generated by the very rapid rotation of the spindles, while at the same time enabling the rotation speed to be increased. In addition, with these spindles the load on the radial bearing is reduced.
If an excessive braking force is exerted on spindles of this type, the spindles can rock angularly (on the upper tip of the spindles) or can rotate non-axially because of said relative elasticity, which causes the spindles to flex when under braking force. This can have repercussions on the adjacent spindles, which can lose rotational speed with consequent breakage of the relative threads. In this respect, the pressing force transmitted onto the drive belt by virtue of the relative elasticity of the spindles can shift it into a position which makes its driving contact with the adjacent spindles precarious, so reducing their rotational speed or making it irregular.